Thank you for your inquiry.
There have been isolated, but not well standardized, attempts to skin test to nitrofurantoin. The first of these that I could find with a search of the literature was a German article. The reference is copied for you below.
There was another case report of an attempt to skin test to nitrofurantoin. This attempt was unsuccessful because the author could not get the capsule contents to dissolve in saline. I have copied the link to this brief report below as well.
Finally, there is an article in the British Journal of Dermatology which looked at various in vivo methods to test for patients with suspected drug allergies to multiple agents. Nitrofurantoin was included amongst these drugs, and prick tests were done with what appears to be a 1:1 dilution with saline. Then it appears also that some intradermal tests were done with further tenfold dilutions of this drug. However, as noted, these references report only small numbers of patients, and the protocols employed have not been well standardized.
Should you wish to proceed with skin testing, the most helpful of these three references would be the one appearing in the British Journal of Dermatology.
Thank you again for your inquiry and we hope this response is helpful to you.
Dtsch Med Wochenschr. 1972 Feb 18;97(7):256-7.
[Anaphylactic shock following oral administration of nitrofurantoin and demonstration of reagins using the heterologous intracutaneous test (Prausnitz-Küstner)].
[Article in German]
Tykal P, Wilms H
Gary Stadtmauer, MD, Allergy & Clinical
The usefulness of skin tests to prove drug hypersensitivity
British Journal of Dermatology
Volume 152, Issue 5, pages 968–974, May 2005
Phil Lieberman, M.D.